v4.19.13 snapshot.
diff --git a/fs/fs_pin.c b/fs/fs_pin.c
new file mode 100644
index 0000000..a6497cf
--- /dev/null
+++ b/fs/fs_pin.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include "internal.h"
+#include "mount.h"
+
+static DEFINE_SPINLOCK(pin_lock);
+
+void pin_remove(struct fs_pin *pin)
+{
+ spin_lock(&pin_lock);
+ hlist_del_init(&pin->m_list);
+ hlist_del_init(&pin->s_list);
+ spin_unlock(&pin_lock);
+ spin_lock_irq(&pin->wait.lock);
+ pin->done = 1;
+ wake_up_locked(&pin->wait);
+ spin_unlock_irq(&pin->wait.lock);
+}
+
+void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
+{
+ spin_lock(&pin_lock);
+ if (p)
+ hlist_add_head(&pin->s_list, p);
+ hlist_add_head(&pin->m_list, &real_mount(m)->mnt_pins);
+ spin_unlock(&pin_lock);
+}
+
+void pin_insert(struct fs_pin *pin, struct vfsmount *m)
+{
+ pin_insert_group(pin, m, &m->mnt_sb->s_pins);
+}
+
+void pin_kill(struct fs_pin *p)
+{
+ wait_queue_entry_t wait;
+
+ if (!p) {
+ rcu_read_unlock();
+ return;
+ }
+ init_wait(&wait);
+ spin_lock_irq(&p->wait.lock);
+ if (likely(!p->done)) {
+ p->done = -1;
+ spin_unlock_irq(&p->wait.lock);
+ rcu_read_unlock();
+ p->kill(p);
+ return;
+ }
+ if (p->done > 0) {
+ spin_unlock_irq(&p->wait.lock);
+ rcu_read_unlock();
+ return;
+ }
+ __add_wait_queue(&p->wait, &wait);
+ while (1) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ spin_unlock_irq(&p->wait.lock);
+ rcu_read_unlock();
+ schedule();
+ rcu_read_lock();
+ if (likely(list_empty(&wait.entry)))
+ break;
+ /* OK, we know p couldn't have been freed yet */
+ spin_lock_irq(&p->wait.lock);
+ if (p->done > 0) {
+ spin_unlock_irq(&p->wait.lock);
+ break;
+ }
+ }
+ rcu_read_unlock();
+}
+
+void mnt_pin_kill(struct mount *m)
+{
+ while (1) {
+ struct hlist_node *p;
+ rcu_read_lock();
+ p = READ_ONCE(m->mnt_pins.first);
+ if (!p) {
+ rcu_read_unlock();
+ break;
+ }
+ pin_kill(hlist_entry(p, struct fs_pin, m_list));
+ }
+}
+
+void group_pin_kill(struct hlist_head *p)
+{
+ while (1) {
+ struct hlist_node *q;
+ rcu_read_lock();
+ q = READ_ONCE(p->first);
+ if (!q) {
+ rcu_read_unlock();
+ break;
+ }
+ pin_kill(hlist_entry(q, struct fs_pin, s_list));
+ }
+}